Projection system including intrinsic polarizer

ABSTRACT

A projection system including an intrinsic polarizer is disclosed. The projection system includes a light source producing illumination light, an imager disposed to receive the illumination light, and a projection lens disposed to receive the illumination light from the imager. The imager includes an intrinsic polarizer. An intrinsic polarizer stack including a U.V. curable adhesive is also disclosed.

CROSS-REFERENCE

This application claims priority to Provisional U.S. Application No.60/639,990 filed Dec. 29, 2004, which is incorporated by reference inits entirety herein.

BACKGROUND

This invention generally relates to projection systems includingintrinsic polarizers. Specifically, the invention relates totransmissive or reflective projection systems including intrinsicpolarizers.

Projection display systems usually include a source of light,illumination optics, an image-forming device, projection optics and aprojection screen. The illumination optics collect light from a lightsource and direct it to one or more image-forming devices in apredetermined manner. The image-forming device(s), controlled by anelectronically conditioned and processed video signal (typicallydigital), produces an image corresponding to the video signal.Projection optics then magnify the image and project it onto theprojection screen. White light sources, such as arc lamps, inconjunction with color wheels have been used as light sources forprojection display systems. However, recently, light emitting diodes(LEDs) were introduced as an alternative. Some advantages of LED lightsources include longer lifetime, higher efficiency, superior thermalcharacteristics and better color gamut.

Examples of image-forming devices include liquid crystal panels, such asa liquid crystal on silicon device (LCOS). In liquid crystal panels, thealignment of the liquid crystal material is controlled incrementally(pixel-to-pixel) according to the data corresponding to a video signal.Depending on the alignment of the liquid crystal material, polarizationof the incident light may be altered by the liquid crystal structure.Thus, with appropriate use of polarizers or polarizing beam splitters,dark and light regions may be created, which correspond to the inputvideo data.

Another type of an image-forming device is a high temperaturepolysilicon liquid crystal device (HTPS-LCD). HTPS-LCD also includes aliquid crystal layer, in which the alignment can be controlledincrementally (pixel-to-pixel), as determined by the data correspondingto a video signal. The liquid crystal layer is sandwiched between twoglass substrates, each with an array of transparent electrodes on them,thus being adapted for operation in transmission. Typically, at thecorner of each HTPS-LCD pixel, there is a microscopic thin filmtransistor.

Current HTPS and LCOS based projection systems are enabled by the usedye-type polarizers. However, dye-type polarizers have limitations suchas, for example, environmental instability, limited light transmissionand/or degradation under high light flux.

SUMMARY

Generally, the present invention relates to improved projection systemsincluding intrinsic polarizers. Specifically, the invention relates totransmissive or reflective projection systems including intrinsicpolarizers.

In one illustrative embodiment, a projection system including anintrinsic polarizer is disclosed. The projection system includes a lightsource producing illumination light, an imager disposed to receive theillumination light, and a projection lens disposed to receive theillumination light from the imager. The imager includes an intrinsicpolarizer. An intrinsic polarizer stack is also disclosed.

In another illustrative embodiment, a projection system includes a lightsource producing illumination light, an imager disposed to receive theillumination light, and a projection lens disposed to receive theillumination light from the imager. The imager includes an intrinsicpolarizer disposed on a liquid crystal light modulator, a pressuresensitive adhesive disposed between the intrinsic polarizer and theliquid crystal light modulator, and a U.V curable adhesive disposed onthe intrinsic polarizer.

In a further illustrative embodiment, a polarizer stack includes anintrinsic polarizer film, a substrate, and a U.V. cured adhesivedisposed between the intrinsic polarizer film and the substrate. TheU.V. cured adhesive includes a silane.

These and other aspects of the present application will be apparent fromthe detailed description below. In no event, however, should the abovesummaries be construed as limitations on the claimed subject matter,which subject matter is defined solely by the attached claims, as may beamended during prosecution.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 schematically illustrates an embodiment of a transmissiveprojection system;

FIG. 2 schematically illustrates an embodiment of a reflectiveprojection system;

FIG. 3 schematically illustrates an embodiment of an intrinsic polarizerstack;

FIG. 4 schematically illustrates another embodiment of an intrinsicpolarizer stack;

FIG. 5 schematically illustrates an embodiment of a transmissive imager;and

FIG. 6 schematically illustrates an embodiment of a reflective imager.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention.

DETAILED DESCRIPTION

The present invention is believed to be applicable generally toprojection systems including intrinsic polarizers. Specifically, theinvention relates to transmissive or reflective projection systemsincluding intrinsic polarizers. These examples, and the examplesdiscussed below, provide an appreciation of the applicability of thedisclosed projection systems, but should not be interpreted in alimiting sense.

The term “polymer” will be understood to include polymers, copolymers(e.g., polymers formed using two or more different monomers), oligomersand combinations thereof, as well as polymers, oligomers, or copolymers.Both block and random copolymers are included, unless indicatedotherwise.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein.

Weight percent, percent by weight, % by weight, and the like aresynonyms that refer to the concentration of a substance as the weight ofthat substance divided by the weight of the composition and multipliedby 100.

The recitation of numerical ranges by endpoints includes all numberssubsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3,3.80, 4, and 5).

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” include plural referents unless the contentclearly dictates otherwise. Thus, for example, reference to acomposition containing “a silane” includes a mixture of two or moresilanes. As used in this specification and the appended claims, the term“or” is generally employed in its sense including “and/or” unless thecontent clearly dictates otherwise.

Projection systems typically include a transmissive or a reflectiveimager, also referred to as a light valve or light valve array, whichimposes an image on a light beam. Transmissive imagers can betranslucent and allow light to pass through. Reflective imagers, on theother hand, reflect only selected portions of the input beam to form animage.

A single imager may be used for forming a monochromatic image or a colorimage. Multiple imagers (two, three, four, or more) can be used forforming a color image, where the illuminating light is split intomultiple (two, three, four, or more) beams of different color. An imageis imposed on each of the beams individually, which are then recombinedto form a full color image.

FIG. 1 schematically illustrates an embodiment of a transmissiveprojection system 100. In one embodiment, illumination light 104 from alight source or lamp 106 is focused into a tunnel integrator 102.Illumination light 112 exiting the tunnel integrator 102 is collimatedby a condensing lens 114 and then passes through an imager field lens118, a transmissive imager 120 and a projection lens 122 to a screen124. The transmissive imager 120 includes an intrinsic polarizerdisposed within an optical path of the illumination light. One or moreintrinsic polarizers can be disposed prior to and/or after the imager120. The light source 106 may include, for example, a halogen lamp, ahigh pressure mercury arc lamp, a metal halide arc lamp, LED, or someother type of source for generating the illuminating light 104.

FIG. 2 schematically illustrates an embodiment of a reflectiveprojection system 200. The projection system 200 includes a light source206 that directs illumination light 204 to a tunnel integrator 202 andto lenses 226 a and 226 b and is then transmitted via a polarizingbeamsplitter 224 onto a reflective imager 220, to a projection lens 222,then to a screen (not shown.) The reflective imager 220 includes anintrinsic polarizer disposed within an optical path of the illuminationlight. One or more intrinsic polarizers can be disposed prior to and/orafter the imager 220. The light source 206 may include, for example, ahalogen lamp, a high pressure mercury arc lamp, a metal halide arc lamp,LED, or some other type of source for generating the illuminating light204.

The imagers described herein include an intrinsic polarizer positionedwithin the optical path of illumination light. The intrinsic polarizercan be positioned before and/or after the imager and may be disposedadjacent to the imager. The term “adjacent” refers to an element beingdisposed on, or spaced away from the imager. In some embodiments, theintrinsic polarizer is adhered to the imager with an adhesive. In otherembodiments, the intrinsic polarizer is spaced away from the imager withor without one or more layers of material.

Polarizers in the form of synthetic polarizing films exhibit comparativeease of manufacture and handling and comparative ease with which theymay be incorporated into projection systems including imagers. Ingeneral, plane polarizing films have the property of selectively passingradiation vibrating along a given electromagnetic radiation vector andabsorbing electromagnetic radiation vibrating along a secondelectromagnetic radiation vector based on the anisotropic character ofthe transmitting film medium. Plane polarizing films include dichroicpolarizers, which are absorbing plane polarizers utilizing the vectorialanisotropy of their absorption of incident light waves. The term“dichroism” refers to the property of differential absorption of thecomponents of incident light, depending on the vibration directions ofthe component light waves. Light entering a dichroic plane polarizingfilm encounters two different absorption coefficients along transverseplanes, one coefficient being high and the other coefficient being low.Light emerging from a dichroic film vibrates predominantly in the planecharacterized by the low absorption coefficient.

Dichroic plane polarizing films include H-type (iodine) polarizers anddyestuff polarizers. For example, an H-type polarizer is a syntheticdichroic sheet polarizer including a polyvinyl alcohol-iodine complex.Such a chemical complex is referred to as a chromophore. The basematerial of an H-type polarizer is a water-soluble high molecular weightsubstance, and the resulting film has relatively low moisture and heatresistance and tends to curl, peel or otherwise warp when exposed toambient atmospheric conditions. Further, H-type polarizers areinherently unstable, and require protective cladding, e.g., layers ofcellulose triacetate, on both sides of the polarizer to preventdegradation of the polarizer in a normal working environment such as ina liquid crystal display.

In contrast to H-type polarizers and other similar synthetic dichroicplane polarizers are intrinsic polarizers. Intrinsic polarizers polarizelight due to the inherent chemical structure of the base material usedto form the polarizer. Such intrinsic polarizers are also typically thinand durable. Examples of intrinsic polarizers are K-type polarizers.

A K-type polarizer is a synthetic dichroic plane polarizer based onmolecularly oriented polyvinyl alcohol (PVA) sheets or films with abalanced concentration of light-absorbing chromophores. A K-typepolarizer derives its dichroism from the light absorbing properties ofits matrix, not from the light-absorbing properties of dye additives,stains, or suspended crystalline materials. Thus, a K-type polarizer mayhave both good polarizing efficiency and good heat and moistureresistance. A K-type polarizer may also be very neutral with respect tocolor.

An improved K-type polarizer, referred to as a KE polarizer, ismanufactured by 3M Company, Norwood, Mass. The KE polarizer has improvedpolarizer stability under severe environmental conditions, such as hightemperatures and high humidity. In contrast to H-type polarizers, inwhich the light absorption properties are due to the formation of achromophore between PVA and tri-iodide ion, KE polarizers are made bychemically reacting the PVA by an acid catalyzed, thermal dehydrationreaction. The resulting chromophore, referred to as polyvinylene, andthe resulting polymer may be referred to as a block copolymer of vinylalcohol and vinylene. Intrinsic polarizers are described in: U.S. Pat.Nos. 5,666,223; 5,973,834; 6,549,335; 6,630,970; 6,808,657; 6,814,899;US2003/0189264; US2003/0189275; US2003/0190491; US2004/0241480, all ofwhich are incorporated by reference herein.

For H-type polarizers, stability is generally achieved by sandwichingthe polarizer between two plastic substrates, such as two layers ofcellulose triacetate, one on each side of the polarizer. However, evenin these structures the application of heat, humidity and/or vacuum canadversely affect the properties of the polarizer. In contrast, K-typepolarizers such as KE polarizers do not need to be sandwiched betweensheets of cellulose triacetate. The polyvinylene chromophore of the KEpolarizer is a stable chemical entity, since the chromophore isintrinsic to the polymer molecule. This chromophore is thermally stableas well as resistant to attack from a wide range of solvents andchemicals, when integrated into a cross-linked polyvinyl alcohol matrix.A K-type polarizer such as a KE polarizer has several advantages overother types of polarizers currently used in projection systems, e.g.,iodine and dyestuff polarizers. K-type polarizers have more durablechromophores, are thinner, and may be designed with variabletransmission levels. Most notably, K-type polarizers such as KEpolarizers may be used in applications that require high performanceunder severe environmental conditions, including high temperatures, highhumidity and high flux (e.g., light intensity), such as, for example, 85degrees Celsius and 85% relative humidity, for extended periods of time.Under such environmental conditions, the stability of H-type or iodinepolarizers is greatly reduced, thus limiting their usefulness inapplications such as projection systems. Due to the inherent chemicalstability of K-type polarizers, a wide variety of adhesive formulations,including pressure sensitive adhesives, can be applied directly toK-type polarizers. Further, a single-sided plastic support is adequateto give physical support for K-type polarizers, and since this supportcan be located outside of the optical path of the liquid crystal displaycell, it need not be optically isotropic and lower-cost substrates suchas polyethylene terephthalate (PET) are acceptable alternatives.Moreover, the ability to construct single-sided laminates allows theoptical structures to be thinner, allowing for additional flexibility inthe design and manufacture of flat panel display elements. Theseadvantages of K-type polarizers may be used in a wide variety of opticalapplications, including projection systems. Thus, it is believed thatdichroic plane polarizing films include H-type (iodine) polarizers anddyestuff polarizers currently used in projection systems can be replacedwith K or KE-type polarizers.

Some advantages of using K or KE polarizers in a projection systeminclude:

1). Optics. KE polarizer can be produced with optics closelyapproximating iodine polarizers. However, when compared to dye-typepolarizers of a given efficiency, KE polarizers may exhibitsignificantly enhanced transmission. Brightness is a factor inprojection system design and the potential for enhanced transmission oflight through the polarizer is a benefit.

2). Durability. KE polarizer maintains its optical properties whenexposed to extremes of heat and humidity and does not suffer from thebleaching or browning typical of iodine or dye-type polarizers. KEpolarizers used in projection optics will show negligible change withtime and the brightness and contrast of the projected image will bemaintained.

3). Structure. Due to the inherent durability of KE polarizers, the useof encapsulating substrates such as TAC is not required. In a projectionsystem it is advantageous to eliminate as many organic layers aspossible as they are subject to degradation under the high intensityillumination. Due to the inherent chemical stability of the KE polarizerit is expected that the material will be able to withstand a higher heatload than dye-containing materials.

FIG. 3 schematically illustrates an embodiment of an intrinsic polarizerstack 300 useful in projection systems. An intrinsic polarizer 310 isshown disposed on a substrate 330 with an adhesive layer 320. Anoptional anti-reflective layer 360 is disposed on the intrinsicpolarizer 310.

The intrinsic polarizer 310 can be a K or KE-type polarizer, asdescribed above. The intrinsic polarizer 310 can have any usefulthickness. In some embodiments, the intrinsic polarizer 310 has athickness in a range from 5 to 100 micrometers, or 10 to 50 micrometers,or 20 to 40 micrometers.

The substrate 330 can be formed of any useful material. In someembodiments, the substrate 330 is formed of a polymeric material suchas, for example, cellulose triacetate, polycarbonate, polyacrylate,polypropylene, or polyethylene terephthalate. In some embodiments, thesubstrate 330 is formed of an inorganic material such as, for example,quartz, glass, sapphire, YAG, or mica.

The substrate 330 can have any useful thickness. In some embodiments,the substrate 330 has a thickness in a range from 10 micrometers orgreater, or 10 to 1000 micrometers, or 25 to 500 micrometers, or 50 to250 micrometers. In other embodiments, the substrate 330 has a thicknessin a range from 10 micrometers to 20 centimeters. In some embodiments,the substrate 330 is planar, in other embodiments, the substrate 330 isnon-planar. In some embodiments, the substrate 330 has opticalfunctionality such as retardation or wavelength selectivity.

In some embodiments, the substrate 330 is a release liner. The releaseliner 330 can be formed of any useful material such as, for example,polymers or paper and may include a release coat. Suitable materials foruse in release coats include, but are not limited to, fluoropolymers,acrylics and silicones designed to facilitate the release of the releaseliner 330 from the adhesive 320.

The adhesive 320 can be formed of any useful material. In someembodiments, the adhesive 320 is formed of a urethane, epoxy, or acrylicmaterial and can be curable. In one embodiment, the adhesive 320 is aU.V. curable adhesive that includes a silane.

In one embodiment, the adhesive 320 is a pressure sensitive adhesive.The pressure sensitive adhesive 320 can be formed of any usefulmaterial. In some embodiments, the pressure sensitive adhesive 320 is anacrylic pressure sensitive adhesive. A partial listing of usefulacrylate pressure sensitive adhesives includes commercially availableadhesives available from Soken Chemical Company, Japan, under thetradename Soken 2106, Soken 1885, Soken 2263 and Soken 2065.

The adhesive 320 can have any useful thickness. In some embodiments, theadhesive 320 has a thickness in a range from 1 to 100 micrometers, or 5to 75 micrometers, or 10 to 50 micrometers, or 20 to 40 micrometers. Inother embodiments, the adhesive 320 has a thickness in a range from 0.1to 20 micrometers, or 1 to 15 micrometers, or 1 to 10 micrometers.

An optional anti-reflective coating 360 can be applied directly to theintrinsic polarizer 310. The anti-reflection coating 360 may include aplurality of polymer layers or inorganic layers. In some embodiments,the anti-reflection coating 360 has a thickness of less than 1micrometer and is an inorganic material such as ITO or A-ITO. Ananti-reflection coating 360 may also have one or more anti-reflectionlayers, with the layers having alternating high and low indices ofrefraction, because the optical performance of an anti-reflection filmincreases with the number of layers. Such a multilayer anti-reflectionfilm preferably has a series of highly uniform polymer or inorganiclayers formed by web coating, sputtering, e-beam, vapor deposition orcombinations thereof. In some embodiments, an optional anti-reflectivecoating (not shown) can be applied to a surface of the substrate 330.

FIG. 4 schematically illustrates an embodiment of an intrinsic polarizerstack 400 useful in projection systems. An intrinsic polarizer 410 isshown disposed on a first substrate 450 with a first adhesive 440. Asecond adhesive 420 is disposed on an opposing side of the intrinsicpolarizer 410 and between the intrinsic polarizer 410 and a secondsubstrate 430. An optional anti-reflective coating 460 is disposed onthe first substrate 450.

The intrinsic polarizer 410 can be a K or KE-type polarizer, asdescribed above. The intrinsic polarizer 410 can have any usefulthickness. In some embodiments, the intrinsic polarizer 410 has athickness in a range from 5 to 100 micrometers, or 10 to 50 micrometers,or 20 to 40 micrometers.

The first substrate 450 can be formed of any useful material. In someembodiments, the first substrate 450 is formed of a polymeric materialsuch as, for example, cellulose triacetate, polycarbonate, polyacrylate,polypropylene, or polyethylene terephthalate. In other embodiments, thefirst substrate 450 is formed of an inorganic material such as, forexample, quartz, glass, sapphire, YAG, or mica.

The first substrate 450 can have any useful thickness. In someembodiments, the first substrate 450 has a thickness in a range from 10micrometers or greater, or 10 to 1000 micrometers, or 25 to 500micrometers, or 50 to 250 micrometers. In other embodiments, the firstsubstrate 450 has a thickness in a range from 10 micrometers to 20centimeters. In some embodiments, the first substrate 450 is planer, inother embodiments, the first substrate 450 is non-planar. In someembodiments, the first substrate 450 has optical functionality such asretardation or wavelength selectivity.

The second substrate 430 can be formed of any useful material. In someembodiments, the second substrate 430 is formed of a polymeric materialsuch as, for example, cellulose triacetate, polycarbonate, polyacrylate,polypropylene, or polyethylene terephthalate. In other embodiments, thesecond substrate 430 is formed of an inorganic material such as, forexample, quartz, glass, sapphire, YAG, or mica.

The second substrate 430 can have any useful thickness. In someembodiments, the second substrate 430 has a thickness in a range from 10micrometers or greater, or 10 to 1000 micrometers, or 25 to 500micrometers, or 50 to 250 micrometers. In other embodiments, the secondsubstrate 430 has a thickness in a range from 10 micrometers to 20centimeters. In some embodiments, the second substrate 430 is planar, inother embodiments, the second substrate 430 is non-planar. In someembodiments, the second substrate 430 has optical functionality such asretardation or wavelength selectivity.

In some embodiments, the second substrate 430 is a release liner. Therelease liner 430 can be formed of any useful material such as, forexample, polymers or paper and may include a release coat. Suitablematerials for use in release coats include, but are not limited to,fluoropolymers, acrylics and silicones designed to facilitate therelease of the release liner 430 from the second adhesive 420.

The first adhesive 440 can be formed of any useful material. In someembodiments, the first adhesive 440 is formed of a urethane, epoxy, oracrylic material and can be curable. In one embodiment, the firstadhesive 440 is a U.V. curable adhesive that includes a silane. Apartial listing of useful U.V. curable adhesives includes: isocyanatebased adhesives such as Araldite 2026A/B available from HuntsmanAdvanced Materials, Belgium; urethane based adhesives such as Loctite™U-09LV, U-09FL, U-10FL available from Henkel Loctite Corp., Connecticutand OP-44 available from Dymax Corp,. Torrington, Conn.; epoxy basedadhesives such as Hysol E-30CL, Hysol E-05CL available from HenkelLoctite Corp., Connecticut. In one embodiment, the silane isN-beta-(aminoethyl)-gamma-aminopropyltriethoxysilane, known as Silquest™A-1120 silane available from GE Silicones, WV. The silane can be addedto the adhesive at any useful ratio of adhesive:silane such as, forexample, 100:1 to 10:1 ratio by wt %.

In another embodiment, the first adhesive 440 is a pressure sensitiveadhesive. The pressure sensitive adhesive can be formed of any usefulmaterial. In some embodiments, the pressure sensitive adhesive is anacrylic pressure sensitive adhesive. A partial listing of usefulacrylate pressure sensitive adhesives includes commercially availableadhesives available from Soken Chemical Company, Japan, under thetradename Soken 2106, Soken 1885, Soken 2263 and Soken 2065.

The first adhesive 440 can have any useful thickness. In someembodiments, the first adhesive 440 has a thickness in a range from 0.1to 20 micrometers, or 1 to 15 micrometers, or 1 to 10 micrometers.

The second adhesive 420 can be formed of any useful material. In someembodiments, the second adhesive 420 is formed of an acrylic material.In some embodiments, the second adhesive 420 is an acrylic pressuresensitive adhesive. A partial listing of useful acrylate pressuresensitive adhesives includes commercially available adhesives availablefrom Soken Chemical Company, Japan, under the tradename Soken 2106,Soken 1885, Soken 2263 and Soken 2065. The second adhesive 420 can haveany useful thickness. In some embodiments, the second adhesive 420 has athickness in a range from 1 to 100 micrometers, or 10 to 75 micrometers,or 20 to 40 micrometers.

An optional anti-reflective coating 460 can be applied to the firstsubstrate 450. The anti-reflection coating 460 may include a pluralityof polymer layers or inorganic layers. In some embodiments, theanti-reflection coating 460 has a thickness of less than 1 micrometerand is an inorganic material such as ITO or A-ITO. An anti-reflectioncoating 460 may also have one or more anti-reflection layers, with thelayers having alternating high and low indices of refraction, becausethe optical performance of an anti-reflection film increases with thenumber of layers. Such a multilayer anti-reflection film preferably hasa series of highly uniform polymer or inorganic layers formed by webcoating, sputtering, e-beam, vapor deposition or combinations thereof.In some embodiments, an optional anti-reflective coating (not shown) canbe applied to a surface of the first substrate 450 and/or secondsubstrate 430. The optional anti-reflective coating can be applied toany surface that interfaces with air in order to reduce undesirablereflections.

FIG. 5 schematically illustrates an embodiment of a transmissive imager500. A liquid crystal cell 505 is shown between two intrinsic polarizers510. The intrinsic polarizers 510 can be separated from the liquidcrystal cell 505 by one or more layers or be spaced away from the liquidcrystal cell 505. In the embodiment shown in FIG. 5, a second adhesivelayer 520 is disposed between the liquid crystal cell 505 and theintrinsic polarizer 510. A first substrate 550 is bonded to theintrinsic polarizer 510 with a first adhesive layer 540. An optionalanti-reflective coating 560 can be applied to the second substrate 550.The intrinsic polarizer 510, second adhesive layer 520, first substrate550, first adhesive layer 540, and anti-reflection coating 560 are alldescribed above with FIG. 4. In one embodiment, the imager 500 includes,a K or KE polarizer 510, a pressure sensitive adhesive layer 520, anunhydrolyzed cellulose triacetate substrate 550, and a U.V. curableadhesive 540.

FIG. 6 schematically illustrates an embodiment of a reflective imager600. A liquid crystal cell 605 is shown between an intrinsic polarizer610 and a reflective mirror 606. The intrinsic polarizer 610 and thereflective mirror 606 can be separated from the liquid crystal cell 605by one or more layers or be spaced away from the liquid crystal cell605. In the embodiment shown in FIG. 6, a second adhesive layer 620 isdisposed between the liquid crystal cell 605 and the intrinsic polarizer610. A first substrate 650 is bonded to the intrinsic polarizer 610 witha first adhesive layer 640. An optional anti-reflective coating 660 canbe applied to the first substrate 650. The intrinsic polarizer 610,second adhesive layer 620, second substrate 650, the first adhesivelayer 640, and anti-reflection coating 660 are all described above withFIG. 4. In one embodiment, the imager 600 includes, a K or KE polarizer610, a pressure sensitive adhesive layer 620, an unhydrolyzed cellulosetriacetate substrate 650, and a U.V. curable adhesive 640.

Further Discussion

Polarizer films used in projection system imagers can be laminated onboth sides to cellulose triacetate substrates using various formulationsof aqueous polyvinyl alcohol (PVA) adhesive (“dopes”). Hydrolysis of thetriacetate surface has been required to provide good adhesion to theaqueous PVA adhesive, where the chemical hydrolysis of the triacetatesurface generally increases adhesion to the PVA adhesive. Thisconstruction can then be laminated directly to glass, or to otherplastic films and then to glass, using pressure sensitive adhesives, orother thermoplastic adhesive formulations. Polyvinylene polarizer filmscan also be used in similar constructions.

These constructions are often not physically or optically durable ateither high temperature, high temperature/high humidity, or underintense light exposure, because: a) the highly oriented polarizer tendsto shrink which causes unacceptable defects such as bubbling,delamination, or stress lines, or b) the polarizer and/or associatedadhesives fade or darken under intense light exposure. In addition, thehydrolysis of triacetate is costly and tends to introduce several typesof defects into optical stacks.

Liquid ultraviolet (UV) cured adhesive formulations, described herein,can be used to replace the aqueous dope fluids mentioned above. Thesecan be used on one or both sides of the polarizer to bond it to variousplastic substrates, even non-hydrolyzed triacetate. The disclosed U.V.cured adhesive formulations adhere well to non-hydrolyzed triacetate,eliminating the need for a triacetate hydrolysis process step.Constructions can be obtained which when laminated to glass, physicallysurvive severe conditions of temperature, humidity, and or lightexposure. In many embodiments, silane adhesion promoters are useful toincrease adhesion of the adhesive to both the polarizer and triacetatesubstrates.

In some embodiments, the substrate 330, 450, 430 described herein is acellulose triacetate material having a hydrolyzed or non-hydrolyzedsurface. In one embodiment, the substrate 330, 450, 430 is cellulosetriacetate with a non-hydrolyzed surface. The disclosed U.V. curedadhesive formulations adhere well to non-hydrolyzed triacetate,eliminating the need for a triacetate hydrolysis process step.

A partial listing of useful U.V. curable adhesives useful in thedescribed adhesive layers 320, 440, 420 includes: isocyanate basedadhesives; urethane based adhesives such as Araldite 2026A/B availablefrom Huntsman Advanced Materials, Belgium, Loctite™ U-09LV, U-09FL,U-10FL available from Henkel Loctite Corp., Connecticut and OP-44available from Dymax Corp,. Torrington, Conn.; epoxy based adhesivessuch as Hysol E-30CL, Hysol E-05CL available from Henkel Loctite Corp.,Connecticut; urethane acrylate based adhesives such as Loctite™ 3104,3105, 3107 available from Henkel Loctite Corp., Connecticut; and/oracrylate based adhesives such as Loctite™ 3491 available from HenkelLoctite Corp., Connecticut. In one embodiment, the silane isN-beta-(aminoethyl)-gamma-aminopropyltriethoxysilane, known as Silquest™A-1120 silane available from GE Silicones, WV. The silane can be addedto the adhesive at any useful ratio of adhesive:silane such as, forexample, 100:1 to 10:1 ratio by wt %.

With regard to FIG. 4, an optional anti-reflective coating 470 can beapplied to the second substrate 430. The anti-reflection coating 470 mayinclude a plurality of polymer layers or inorganic layers. In someembodiments, the anti-reflection coating 470 has a thickness of lessthan 1 micrometer and is an inorganic material such as ITO or A-ITO. Ananti-reflection coating 470 may also have one or more anti-reflectionlayers, with the layers having alternating high and low indices ofrefraction, because the optical performance of an anti-reflection filmincreases with the number of layers. Such a multilayer anti-reflectionfilm preferably has a series of highly uniform polymer or inorganiclayers formed by web coating, sputtering, e-beam, vapor deposition orcombinations thereof.

The anti-reflective coatings described herein can be applied to opticalelements or polarizer stacks at any air interface. The anti-reflectivecoatings described herein can be broad band or narrow bandanti-reflective coatings. Broad band anti-reflective coatings can beeffective over at least a majority of the visual spectrum (400-750 nm).Narrow band anti-reflective coatings can be effective over generally onecolor band of the visual spectrum (e.g., 400-500 nm, 500-600 nm, or600-750 nm). In some embodiments, a narrow band anti-reflective coatingis utilized in the polarizer stacks described herein.

FIG. 3 illustrates an asymmetric polarizer stack 300 and FIG. 4illustrates a symmetric polarizer stack 400. In many embodiments, thedual substrate symmetric polarizer stack 400 exhibits less curling thanthe single substrate asymmetric polarizer stack 300. However, when thesubstrates in both polarizer stacks (300, 400) are cellulose triacetate(TAC) the dual substrate symmetric polarizer stack 400 can exhibit moreyellowing under high intensity light flux, than the single substrateasymmetric polarizer stack 300. Thus, when utilizing TAC as a substrate,the amount of possible yellowing must be balanced with the physicalintegrity of the polarizer stacks (300, 400).

Advantages of the invention are illustrated by the following examples.However, the particular materials and amounts thereof recited in theseexamples, as well as other conditions and details, are to be interpretedto apply broadly in the art and should not be construed to unduly limitthe invention.

EXAMPLES

Materials

Substrates:

TAC refers to cellulose triacetate, available from Eastman Kodak, FujiFilm, Lofo, or Island Polymers Industry.

Polarizer:

KE A refers to a KE (7.5× stretch) intrinsic polarizer laminated to TACfilm. A cellulose triacetate (TAC) film and KE-polarizer (20-40micrometer thickness) were laminated together with a curable adhesive(Boscodure 21 available from Bostik Findley, Wauwatosa, Wis.) disposedbetween them. A PSA adhesive was then applied onto the opposite side ofthe KE-polarizer by laminating a release film, pre-coated with PSA(Soken 2106), onto the KE-polarizer. The release film was removed andthe exposed PSA was laminated to a glass slide.

KE B refers to a KE (7.5× stretch) intrinsic polarizer adhered to TACfilm. A cellulose triacetate (TAC) film and KE-polarizer were laminatedtogether with a curable adhesive (Boscodure 21:Vital 3554 in a 4:1 ratioby wt %, both available from Bostik Findley, Wauwatosa, Wis.) disposedbetween them. A PSA adhesive was then applied onto the opposite side ofthe KE-polarizer by laminating a release film, pre-coated with PSA(Soken 2106), onto the KE-polarizer. The release film was removed andthe exposed PSA was laminated to a glass slide.

SHC125U refers to a high contrast dye-stuff polarizer available fromPolatechno Co., Ltd. Japan.

Proj-R refers to a red channel analyzer assembly from 3M MP7740iprojector.

Example 1

Light and Heat Exposure Test:

A 3M MP7740i office projector (having a 150 W UHB bulb) was disassembledso as to expose the light engine components. In order to demonstrate theenhanced durability of KE polarizer the condenser lens just after thepolarization conversion system (PCS) was removed and the slot previouslyoccupied by the lens was used as a mounting position for the testing ofthe polarizer assemblies described below.

Analysis of the PCS indicated that the light exiting the system was inthe approximate ratio of 4:1 pass state to blocked state. The airtemperature in the area of the projector just in front of the PCS wasmeasured to be 110° C.

The polarizers were mounted such that the pass state was maximallytransmitted when the slide assembly was mounted in the projector:

Test Procedure:

The projector was turned on and after a 30 second warm-up the polarizerswere placed in the lens holder, with the polarizer side toward theincident light. The test structures were subjected to the intense lightand heat in 5-minute increments.

The polarizers were characterized for spectral color and transmittancecharacteristics before and after each test.

Color Characteristics:

The color characteristics of each sample were calculated for lighttransmitted through the stack using the wavelength dependenttransmittance measurements made using a Hunterlab Ultrascan XEspectrophotometer. The hue of the transmitted light was subsequentlycalculated, using a D65 illuminant and is listed in the Table below.Color, or hue, is presented according to the CIELAB color system, whichuses co-ordinates: a* and b*. The a* co-ordinate represents red/greencolor and the b* co-ordinate represents yellow/blue color. A positivevalue of a* corresponds to red and a negative value of a* corresponds togreen. A positive value of b* corresponds to yellow and a negative valueof b* corresponds to blue. The (a*, b*) co-ordinate of (0, 0) representsa neutral hue. Furthermore, a value of a* or b* whose magnitude is lessthan 1 results in a barely perceptible change in color from neutral. TheY value is the photopically corrected light transmittance and a decreasein Y represents a darkening in the sample.

Results:

The results are tabulated below in Table 1. Both KE samples exhibitednegligible change in a total of 15 minutes of exposure whereas bothdyestuff samples, including the projection polarizer, showed significantdarkening after 5 minutes of exposure. The SHC125U dyestuff polarizerwas subjected to a further 5 minutes of exposure and exhibited a radicalchange in transmission and color after that period.

TABLE 1 Initial Final Delta Exposure Material Y a* b* Y A* b* Y a* B*Time KE A 42.09 0.26 3.67 42.09 0.42 3.63 0 0.16 −0.04 15 min KE B 42.020.18 3.8 41.12 0.41 4.23 −0.90 0.23 0.43 15 min SHC125U 39.92 −0.17 3.4236.12 0.36 1.58 −3.80 0.53 −1.84  5 min Proj-R 39.95 −1.13 3.85 35.36−2.31 1.90 −4.59 −1.18 −1.94  5 min

Example 2

An intrinsic polarizer stack suitable for use in a projection system wasmade from the following materials.

An anti-reflection coated, 80 micrometer thick cellulose triacetate(TAC) film and a 20-40 micrometer thick, 7.5× stretch, KE polarizer filmmanufactured by 3M was laminated together with a UV curable adhesive,including a silane adhesion promoter, disposed between them. Thelaminated stack was cured using Fusion D bulbs and the resultingthickness of the cured UV adhesive layer was between 2-6 micrometers. APET release film with a layer of acrylic PSA disposed on the surface(such as UV10 available from CP Films, Martinsville, Va.) was thenapplied to the side of the KE polarizer film opposite the TAC film. ThePET release film was removed and the exposed PSA was laminated to aquartz substrate.

Example 3

A retarder plus polarizer stack suitable for use in a projection systemcan be made from the following materials.

A 20-40 micrometer thick, 7.5× stretch, KE polarizer film manufacturedby 3M can be disposed between an 80 micrometer thick cellulosetriacetate (TAC) film and a ½ wave retarder film (available from TejinInds., Japan) and adhered together with an adhesive such as a UVcurable, PSA or epoxy adhesive. The adhesive can be cured by theappropriate method. A PET release film with a layer of acrylic PSAdisposed on the surface (such as UV10 available from CP Films,Martinsville, Va.) can be applied to either the TAC outer surface and/orthe retarder film outer surface. The PET release film can be removed andthe exposed PSA can be laminated to a quartz substrate.

Example 4

A polarizer stack suitable for use in a projection system can be madefrom the following materials.

A 20-40 micrometer thick, 7.5× stretch, KE polarizer film manufacturedby 3M can be disposed between two glass, quartz, or sapphire substratesand adhered together with an adhesive such as a UV curable, PSA or epoxyadhesive. The adhesive can be cured by the appropriate method.

Example 5

In a full structure polarizer film stack, the adhesive used to bond thepolarizer to the substrate should have high adhesion to both elements.If the bond strength to either element is low, the laminatedconstruction will tend to delaminate during cutting, handling, and/orenvironmental testing. Liquid adhesive candidates were tested foradhesion to triacetate and K polarizer using the test procedure listedbelow. Various combinations of U.V. curable adhesives and silaneadhesion promoters were screened by the procedures listed below. In afirst set of tests (Example 5), U.V. adhesives without silane werecompared for bond strength between unhydrolyzed triacetate and Kpolarizer. Results are shown in Table 2.

Test Procedure

-   a. Using two rubber laminating rollers, liquid UV adhesive    candidates were laminated between an unhydrolyzed triacetate    substrate and a K polarizer (resulting in the structure TAC/UV    adhesive/K polarizer).-   b. The constructions were cured through the K polarizer side on a    Fusion UV curing unit (H bulb).-   c. The samples were evaluated on an IMASS Slip/Peel Tester Model    SP-2000 peel force tester by peeling (at 17 inch/min) the two    substrates apart at 90 degree peel angle and measuring peel force in    grams per inch (width of sample).

TABLE 2 Adhesive Peel Force (grams/inch) Loctite 3104 30 Loctite 3105 79Loctite 3107 42 Loctite 3491 2 Dymax OP44 86

Example 6

In the second set of tests (Example 6), four silanes were compared usingLoctite 3105 as the base U.V. curable adhesive, for bond strengthbetween unhydrolyzed triacetate and K polarizer as described in Example5. Results are shown in Table 3.

TABLE 3 Adhesive Peel Force (grams/inch) 25:1 3105:Silane A1120 830 25:13105:3-acryloxypropyl trimethoxysilane 181 25:1 3105:3-(trimethoxysilyl)propyl acrylate 137 25:1 3105:Silane A174 323

Example 7

In the third set of tests (Example 7), different U.V. adhesives wereretested with Silane A1120 present, at two different ratios, for bondstrength between unhydrolyzed triacetate and K polarizer as described inExample 5. Results are shown in Table 4.

TABLE 4 Peel Force (grams/inch) Peel Force (grams/inch) Adhesive 100:1Ratio 25:1 Ratio Loctite 3104 73 Loctite 3105 390 904 Loctite 3107 209145 Loctite 3491 65 Dymax OP44 132 46

Example 8

In the fourth set of tests (Example 8), various ratios of Loctite 3105and Silane A1120 were evaluated with different curing conditions, forbond strength between unhydrolyzed triacetate and K polarizer asdescribed in Example 5. Results are shown in Table 5.

TABLE 5 Adhesive/ U.V. Cure Peel Force Silane Ratio # or Passes(grams/inch) 100:1  1 996 2 350 4 266 50:1 1 771 2 538 4 247 25:1 1 4152 823 4 745 12.5:1   1 182 2 973 4 745

Example 9

The formulation of 25:1 Loctite 3105:Silane A1120, described above, wasused to demonstrate the performance in both oven and projector testing,compared to a competitive projector polarizer structure. The followingconstruction was made in the lab and tested in an oven and in an LCDprojector:

Layer Description Glass 1 mil thick layer of commercially available PSAPSA (Soken 2106) K polarizer 28 micron thick polyvinylene polarizer UVAdhesive 5 micron thick layer of commercially available, 100% solids UVadhesive (Loctite 3105) mixed with Silane A1120 adhesion promoter, 25:1ratio TAC 125 micron hardcoated LOFO TAC, hardcoat on side oppositeadhesive, AR coating on hardcoatOven Testing

-   1. Mixed Loctite 3105 with Silane A1120 (both 100% active) in 25:1    ratio.-   2. Using two nipped rubber rollers, laminated K polarizer to the    uncoated side of TAC which previously had been hardcoated and then    coated with anti-reflection layers.-   3. Transfer laminated Soken 2106 PSA (25 micron thickness) to the    exposed K polarizer.-   4. The PSA side of the construction was laminated between two nipped    rubber rollers to standard glass microscope slides.-   5. The polarizer/glass laminates transmittance were measured on a    Cary 5E spectrophotometer. Included in the output from this    measurement is the sample transmittance using plane polarized light    which is perpendicular to the absorption axis of the polarizer    (“pass” transmittance). This value is referred to as “k1” and is    typically between 80% and 90% for samples of this type.-   6. A sample was then placed in a 120° C. (dry) oven for 28 days, and    then transmittance was re-measured. This resulted in a k1 loss of    3.2%. A comparative sample was also measured. This sample was a    dyestuff polarizer (laminated to a quartz substrate) which was    removed from the blue channel of a commercially available LCD    projector. After 28 days at 120° C., the comparative sample had a k1    loss of 8.5%. Based on analysis of other similar samples, we believe    the construction of this comparative sample to be the following    construction:    -   quartz/PS/triacetate/dope adhesive/dyestuff        polarizer/dope/triacetate/hardcoat/AR.        Projector Testing-   1. Same as step 1 in oven testing.-   2. Same as step 2 in oven testing.-   3. Same as step 3 in oven testing.-   4. Same as step 4 in oven testing, except used quartz substrate    instead of glass.-   5. Same as step 5 in oven testing. For this test, the important    output is k2, which is the transmittance using plane polarized light    which is parallel to the absorption axis of the polarizer (“cross”    transmittance). Typical k2 values for these samples are 0.01-0.03%.-   6. A sample was placed in the green entrance position of a    commercially available LCD projector. The polarization conversion    unit (which polarizes the light emitted by the illuminating bulb)    was removed, resulting in greater light absorption and heating by    the entrance polarizer. The effect of this change is to accelerate    the failure of the polarizing element. K type samples were compared    to the existing dyestuff green polarizer which comes with the    projector, with the following shown in Table 6.

TABLE 6 Sample Projection Time Result Comparative 2 days Completebleaching green Catastrophic k2 increase K-type 2 days k2 increase from0.027% to 0.032% K-type 13 days  k2 increase from 0.027% to 0.038%

The complete disclosure of all patents, patent documents, andpublications cited herein are incorporated by reference. The foregoingdetailed description and examples have been given for clarity ofunderstanding only. No unnecessary limitations are to be understoodtherefrom. The invention is not limited to the exact details shown anddescribed, for variations obvious to one skilled in the art will beincluded within the invention defined by the claims.

1. A polarizer stack comprising: an intrinsic polarizer film; asubstrate; and a U.V. cured adhesive disposed between the intrinsicpolarizer film and the substrate, the U.V. cured adhesive comprising asilane.
 2. A polarizer stack according to claim 1 wherein the intrinsicpolarizer film comprises polyvinylene.
 3. A polarizer stack according toclaim 1 wherein the intrinsic polarizer film is a KE-type polarizerfilm.
 4. A polarizer stack according to claim 1 wherein the substratecomprises a polymeric material.
 5. A polarizer stack according to claim1 wherein the substrate comprises a triacetate material.
 6. A polarizerstack according to claim 1 wherein the substrate comprises anon-hydrolyzed triacetate material.
 7. A polarizer stack according toclaim 1 further comprising a pressure sensitive adhesive layer disposedon the intrinsic polarizer film, the intrinsic polarizer film disposedbetween the pressure sensitive adhesive layer and the U.V. curedadhesive.
 8. A polarizer stack according to claim 1 wherein the U.V.curable adhesive comprises a urethane acrylate based adhesive.
 9. Apolarizer stack according to claim 1 wherein the silane comprisesN-beta-(aminoethyl)-gamma-aminopropyltriethoxysilane.